[MAINT] update PR template to include BEP header

[Remi-Gau]

Closes none

---

• improve readability of PR template message (vertically group list items by topic)
• semantic line break
• add section for BEP PR to include "github admonitions" (started adding those eyetracking BEP and ephys BEP)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 87.79%. Comparing base (1cb92eb) to head (5545e5c). Report is 3 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1797 +/- ## ======================================= Coverage 87.79% 87.79% ======================================= Files 16 16 Lines 1360 1360 ======================================= Hits 1194 1194 Misses 166 166 ```

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